Many commercial products are temperature sensitive and can spoil, deteriorate or lose quality if they suffer sufficient exposure to a freezing temperature that is near or below the freezing point of water. For example, some foodstuffs, such as fruits and salad greens, can spoil, and vaccines, biological and other pharmaceutical products, and medications, can lose potency if exposed to a freezing temperature. In some cases, a cold-sensitive product may suffer a loss of quality owing to exposure to an unduly cold temperature, without exhibiting any clear change in appearance or other overt characteristic.
To help monitor for possible exposure of a host product to a freezing temperature, and a consequent loss of quality, a freeze indicator can be employed. One type of freeze indicator useful for this purpose provides an irreversible optical indication of past exposure of a host product to a freezing or near freezing temperature. The freeze indicator can be associated with a freeze-sensitive host product, for example by attaching the freeze indicator to the host product or a package or container for the host product. The freeze indicator can then monitor temperature conditions similar to those to which the host product is exposed during the distribution of the host product from a supplier to an end user, or for another period of interest.
Various proposals for freeze indicators are known. For example, U.S. Pat. Nos. 7,343,872; 7,490,575 and 7,571,695 and U.S. Patent Application Publication No. 2008/0257251, all having inventors Taylor et al., disclose a variety of freeze indicators and freeze indicator technologies. These patents and patent application publications are referenced herein as the “Taylor et al. patent publications.” Also, U.S. Patent Application Publication No. 2010/0162941, by Lentz et al., referenced herein as the “Lentz et al. patent publication” and No. 2011/0209658 by Smith et al., referenced herein as the “Smith et al. patent publication”, disclose a variety of freeze indicators and freeze indicator technologies. Each of the Taylor et al., Lentz et al. and Smith et al. patent publications is incorporated by reference herein in its entirety.
As described in their specifications the Taylor et al. and Lentz et al patent publications disclose freeze indicators which employ an indicator element including a dispersion of particles in a liquid medium. The indicator element can change appearance irreversibly upon exposure to freezing temperatures, for example as a result of coagulation of the dispersed solid particles, providing a signal that the freeze indicator has been exposed to a freezing temperature.